# std::dec, std::hex, std::oct

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< cpp‎ | io‎ | manip

Defined in header `<ios>` |  |
std::ios_base& dec( std::ios_base& str ); | (1) |
std::ios_base& hex( std::ios_base& str ); | (2) |
std::ios_base& oct( std::ios_base& str ); | (3) |

Modifies the default numeric base for integer I/O.

1) Sets the `basefield` of the stream str to `dec` as if by calling str.setf(std::ios_base::dec, std::ios_base::basefield).
2) Sets the `basefield` of the stream str to `hex` as if by calling str.setf(std::ios_base::hex, std::ios_base::basefield).
3) Sets the `basefield` of the stream str to `oct` as if by calling str.setf(std::ios_base::oct, std::ios_base::basefield).

This is an I/O manipulator. It may be called with an expression such as out << std::hex for any `out` of type std::basic_ostream or with an expression such as in >> std::hex for any `in` of type std::basic_istream.

### Parameters

str | - | reference to I/O stream

### Return value

str (reference to the stream after manipulation).

### Example

Run this code

    #include <bitset>
    #include <iostream>
    #include <sstream>

    int main()
    {
        std::cout << "The number 42 in octal:   " << std::oct << 42 << '\n'
                  << "The number 42 in decimal: " << std::dec << 42 << '\n'
                  << "The number 42 in hex:     " << std::hex << 42 << '\n';
        int n;
        std::istringstream("2A") >> std::hex >> n;
        std::cout << std::dec << "Parsing \"2A\" as hex gives " << n << '\n';
        // the output base is sticky until changed
        std::cout << std::hex << "42 as hex gives " << 42
            << " and 21 as hex gives " << 21 << '\n';

        // Note: there is no I/O manipulator that sets up a stream to print out
        // numbers in binary format (e.g. bin). If binary output is necessary
        // the std::bitset trick can be used:
        std::cout << "The number 42 in binary:  " << std::bitset<8>{42} << '\n';
    }

Output:

    The number 42 in octal:   52
    The number 42 in decimal: 42
    The number 42 in hex:     2a
    Parsing "2A" as hex gives 42
    42 as hex gives 2a and 21 as hex gives 15
    The number 42 in binary:  00101010

### See also

setbase | changes the base used for integer I/O (function)
showbasenoshowbase | controls whether prefix is used to indicate numeric base (function)

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